“I feel like my feet are really pissed off at me, just because of the shoes,” Stewart told PEOPLE at the premiere of her new indie drama Welcome to the Rileys on Friday. “That s been the biggest problem.”

One night earlier, the actress, 20, strutted the carpet at the L.A. premiere of the new Twilight film, Eclipse, which she has been promoting around the world. But she says she s not exhausted by the publicity grind – much the opposite, in fact.

“By the end of the day I actually get really hyper, because it’s then that I have my own time,” she says. “You end up staying up all night and then screwing your morning the next day because you need time to yourself.”

As for her intensely emotional role in Rileys, in which she plays a teenage prostitute, “the subject matter was a lot sadder and emotionally distraught than I’ve ever had to deal with,” says Stewart. “It’s sort of the lowest of the low that I’ve ever had to go.”

Is she worried about how Twi-Hards will respond to seeing her in such a different role?

“Luckily Bella wasn’t my first part,” she says. “I’ve had the chance to really get comfortable with keeping true to why I do what I do, and I can only do it this way. I’m proud of myself – so if other people aren’t, that’s totally cool.”